This invention relates to a mounting substrate suitable, for example, for a power window system for a vehicle as well as to a driving device using such a substrate.
Electronic controls are the main method of control for the likes of a power window of a vehicle, say, for automatically reversing the direction of motion of a window when an inserted object is detected. Thus, a common driving method is to make use of a relay, as disclosed in Japanese Patent Publication Tokkai 10-169311, in a driving device that supplies power appropriately to a motor serving as the power source for such an opening and closing mechanism and is provided with a control circuit including a control means such as a microcomputer. Explained more in detail, such a driving device is comprised of two relays for supplying power to the motor so as to rotate is in a positive direction (say, for a upward motion of a window for opening it) and in a negative direction (say, for a downward motion of the window for closing it), a switch for causing the motor to rotate in the positive or negative direction in response to an operation at an operating section (say, by means of an operating knob) and a control circuit (including a transistor for driving these relays and a one-chip microcomputer for controlling this transistor) for controlling the relays according to an input from this switch.
For the control of a power window, devices capable of a high-level control such as varying the speed of the object of control (such as a glass pane) are beginning to appear in response to the market needs. Such a control device may include a switching element such as a FET provided to a power supply line for the motor such that the switching element can be controlled by pulse width modulation (PWM) at the time of operation of the motor at a specified duty ratio corresponding to the target of control.
Japanese Patent Publication Tokkai 10-201050 discloses an electrical connector case having a separate substrate referred to as a box with an inverted U-shape having an inner-molded bus bar (a metallic circuit conductor) mounted on the upper surface of an insulator substrate. The bus bar of this box forms a major part of the wiring pattern of the power source system, and the fuses and relays of the power source system are attached to the bus bar of the box. Japanese Patent Publication Tokkai 8-11732 discloses a power steering circuit device having a wiring pattern for passing a large current formed by a metallic plate material affixed by molding. A switching element is mounted to a heat-radiating plate apart from a printed circuit board on which a microcomputer is mounted, and this heat-radiating plate and the printed circuit board are superposed with a specified interval in between.
Problems occur with such driving devices with a control capability as described above if the circuit components for the PWM control such as the switching element are simply mounted to the same substrate with the other basic circuit components such as the relays and the switches as described above. In other words, as the device becomes larger in the direction parallel to the substrate, it becomes difficult to fit within a limited space allowable in a vehicle. In the case of a driving device not adapted to carry out the PWM control, furthermore, the structure of the substrate as a whole becomes different and hence the productivity is adversely affected.
With a structure having all of the aforementioned circuit components mounted to an inexpensive printed circuit board of a general kind, heat generated by the circuit components for the PWM control such as the switching element described above cannot be dissipated effectively to the exterior and it is not possible to prevent the overheating of the switching element or other circuits around it. If all of such circuit components are mounted to a substrate formed by resin-molding a metallic plate material (substantially thicker than the conductive layer of the printed substrate) which becomes the circuit conductor, the problem of overheating can be somewhat improved from the case of a printed circuit board because the resistance of the circuit conductor (and especially the current-carrying line for the motor) can be reduced but the device as a whole becomes larger and both the cost and weight will increase.
In view of the above, it may be considered to mount the circuit components for the PWM control to a separate substrate (mounting substrate) and to mount this separate substrate to a main substrate (or the base substrate) to which the basic circuit components are mounted. There are problems, however, to actually produce such a structure. For example, although the heat generated by the circuit components for the PWM control such as switching element must be eliminated efficiently, a simple structure as disclosed in aforementioned Japanese Patent Publication Tokkai 10-201050 is not sufficient. If a heat-radiating plate is additionally provided as disclosed in aforementioned Japanese Patent Publication Tokkai 8-11732, on the other hand, the total number of components becomes large and this affects the production cost adversely.
If the structure is such that another substrate is mounted onto a main substrate, another problem arises regarding the connection between the switch on the main substrate and the operation section by avoiding interferences among the components. In the example of aforementioned Japanese Patent Publication Tokkai 10-201050, it would be difficult to avoid interferences between the connecting part for the switch and the operating knob and another substrate unless the main substrate is made larger in the lateral direction.